Create geofence from point and distance

cockney.geojson

geofence.php

<?php

use Location\Bearing\BearingEllipsoidal;
use Location\Coordinate;
use Location\Formatter\Polygon\GeoJSON;
use Location\Polygon;

// Let's start at the church of St Mary-le-Bow in London...
$maryLeBow = new Coordinate(51.51371421689447, -0.09365209962470467);

// One definition of a London cockney was that they were born in
// earshot of that church's bells. Let's say that the bells ring
// out for 3 miles (around 5000 meters)...
$distance = 5000;

// We can create a polygon to hold our definition of cockney, a geofence
// of 5000 meters around St Mary-le-Bow.
$cockney = new Polygon();

// Create a bearing calculator to use
$calculator = new BearingEllipsoidal();

// Iterate from a starting bearing of 360 (due north) and then decrease
// our bearing by 10 degrees each time. We decrease from 360 rather than
// increase from 0 so that we're following the "right-hand rule" where
// coordinates for outer polygons are in counter-clockwise order.
for ($bearing = 360; $bearing >= 0; $bearing -= 10) {
    // Use the calculator to get a new point 5000 meters from Mary-le-Bow
    // in our bearing direction and add it to the polygon. The result is
    // a 36-point polygon forming a rough circle around the church.
    $cockney->addPoint($calculator->calculateDestination($maryLeBow, $bearing % 360, $distance));
}

// Create a new GeoJSON formatter to output our geofence polygon
echo (new GeoJSON())->format($cockney);